Method for promoting adhesion between dielectric substrates and metal layers

ABSTRACT

The present invention relates to novel processes for metallization of dielectric substrate surfaces applying organosilane compositions followed by oxidative treatment. The method results in metal plated surfaces exhibiting high adhesion between the substrate and the plated metal while at the same time leaves the smooth substrate surface intact.

FIELD OF THE INVENTION

The present invention relates to novel processes for metallization ofdielectric, substrate surfaces applying silane compositions. The methodresults in metal plated surfaces exhibiting high adhesion between thesubstrate and the plated metal while at the same time leaving the smoothsubstrate surface intact.

BACKGROUND OF THE INVENTION

Various methods are known of metallizing dielectric substrate surfaces.In wet chemical methods, the surfaces to be metallised are, after anappropriate preliminary treatment, either firstly catalysed and thenmetallised in an electroless manner and thereafter, if necessary,metallised electrolytically, or are directly electrolyticallymetallised.

In EP 0 616 053 A1 there is disclosed a method for direct metallisationof dielectric substrate surfaces, in which the surfaces are firstlytreated with a cleaner/conditioner solution, thereafter with anactivator solution, for example a palladium colloidal solution,stabilised with tin compounds, and are then treated with a solutionwhich contains compounds of a metal which is more noble than tin, aswell as an alkali hydroxide and a complex former. Thereafter thesurfaces can be treated in a solution containing a reducing agent, andcan finally be electrolytically metallised.

WO 96/29452 concerns a process for the selective or partial electrolyticmetallisation of surfaces of substrates made from electricallynon-conducting i.e. dielectric materials which for the purpose of thecoating process are secured to plastic-coated holding elements. Theproposed process involves the following steps: a) preliminary treatmentof the surfaces with an etching solution containing chromium (VI) oxide;followed immediately by b) treatment of the surfaces with a colloidalacidic solution of palladium-/tin compounds, care being taken to preventprior contact with adsorption-promoting solutions; c) treatment of thesurfaces with a solution containing a soluble metal compound capable ofbeing reduced by tin (II) compounds, an alkali or alkaline earth metalhydroxide, and a complex forming agent for the metal in a quantitysufficient at least to prevent precipitation of metal hydroxides; d)treatment of the surfaces with an electrolytic metallisation solution.Such method is particularly suitable for ABS (acrylbutadience styrole)and ABS/PC (polycarbonate) based plastic substrates.

Alternatively, conductive polymers can be formed on the dielectricsubstrate surface to provide a first conductive layer for subsequentmetal plating of the surface.

US 2004/0112755 A1 describes direct electrolytic metallization ofelectrically non-conducting substrate surfaces comprising bringing thesubstrate surfaces into contact with a water-soluble polymer, e.g. athiophene; treating the substrate surfaces with a permanganate solution;treating the substrate surfaces with an acidic aqueous solution or anacidic microemulsion of aqueous base containing at least one thiophenecompound and at least one alkane sulfonic acid selected from the groupcomprising methane sulfonic acid, ethane sulfonic acid and ethanedisulfonic acid; electrolytically metallizing the substrate surfaces.

U.S. Pat. No. 5,693,209 is directed to a process for directlymetallizing a circuit board having nonconductor surfaces, includesreacting the nonconductor surface with an alkaline permanganate solutionto form manganese dioxide chemically adsorbed on the nonconductorsurface; forming an aqueous solution of a weak acid and of pyrrole or apyrrole derivative and soluble oligomers thereof; contacting the aqueoussolution containing the pyrrole monomer and its oligomers with thenonconductor surface having the manganese dioxide adsorbed chemicallythereon to deposit an adherent, electrically conducting, insolublepolymer product on the nonconductor surface; and directlyelectrodepositing metal on the nonconductor surface having the insolubleadherent polymer product formed thereon. The oligomers areadvantageously formed in aqueous solution containing 0.1 to 200 g/l ofthe pyrrole monomer at a temperature between room temperature and thefreezing point of the solution.

U.S. Pat. No. 4,976,990 relates to the metallization of dielectricsubstrate surfaces, particularly to the electroless metallization ofdielectric through-hole surfaces in double-sided or multi-layer printedcircuit boards. The methods involves roughening the surface andsubsequently applying a silane composition to such treated surface.Substantial roughening of the surface occurs if the process is performedin this sequence of treatment steps. The method disclosed in this patentincludes a micro etching solution used to remove oxide films from themetal foil, lines 61 to 65. The method, however, is not suitable toobtain a good adhesion between the substrate material and a subsequentlyplated metal layer according to a method of the present invention.

A similar method is disclosed in WO 88/02412.

EP 0 322 233 A2 relates to a method for producing ultrafine patterns ofsilver metal films on substrates employing application of apolymerisable silane, diborane containing solutions, etching insolutions containing sodium hydroxide and hydrogen peroxide and finallyapplying the silver metal layer. Such method is not suitable to producean adherent metal film to a substrate according to the method of thepresent invention.

All methods described require substantial roughening of the surface ofthe non-conductive, dielectric substrate prior to metallization toensure sufficient adhesion between the substrate and the plated metallayer. Roughening has generally been considered indispensable because itis used to prepare the surface of the dielectric substrate. This isbecause roughening has been considered requisite to achieve goodadhesion between the substrate and the metal layer.

However, a rough surface imparts the functionality of the metal platedsurface, e.g with regards to its use as conductor lines in electronicsapplications.

The ongoing miniaturization of features of HDI printed circuit boards,IC substrates and the like requires more advanced manufacturing methodsthan conventional methods such as formation of circuitry by a print andetch method. Such features require that the surface of the substrate isroughened to a limited degree only.

SUMMARY OF THE INVENTION

Thus, it is an object of the present invention to provide a method formetallization of dielectric substrate surfaces without substantiallyroughening the surface while still obtaining a high adhesion between thesubstrate and the metal layer.

This object is achieved by a method for treating a surface of adielectric substrate to prepare said surface for subsequent wet chemicalmetal plating, such method comprising in this order the steps of

-   -   (i) treating said surface with a solution comprising at least        one organosilane compound;    -   (ii) treating said surface with a solution comprising an        oxidizing agent selected from aqueous acidic or alkaline        solutions of permanganate. and followed by    -   (iii) metallizing the substrate after step (ii) with a wet        chemical plating method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a method for manufacture of fine line circuitry known inthe art as semi-additive process (SAP).

FIG. 2 shows a surface after permanganate treatment of GX92 substratematerial according to example P12.

FIG. 3 shows a surface after permanganate treatment of GX92 substratematerial treated with an alkaline permanganate solution according toconditions known in the state of the art.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention the substrate is first treated instep (i) with a composition containing an organosilane compound.

The organosilane compound is applied as a solution, preferably asolution of an organic solvent having a high boiling point, preferablyin the range of 60 to 250° C. and more preferred in the range of 80 to200° C. Organic solvents within the meaning of this invention are polarorganic solvents suitable to dissolve silane compounds.

Suitable organic solvents comprise alcohols, ethers, amines, andacetates. Examples are ethanol, 2-propanol, tetrahydrofuran, ethyleneglycol, diethyleneglycol, 2-isopropoxyethanol (IPPE),di(propyleneglycol)methyletheracetate (DPGMEA), 2-ethyl-1-hexanol,glycerine, dioxin, butyrolacton, N-methyl pyrrolidone (NMP), dimethylformamide, dimethylacetamide, ethanolamine, propylene glycol methylether acetate (PMA), half ethers and half esters of ethylene glycols.

The concentration of the organosilane can vary over a wide rangedepending on the application and the specific organosilane compound. Thesuitable concentration can be obtained by routine experiments. Suitableconcentration generally vary between as low as 0.2 wt. % to 30 wt. %,preferably between 0.5 wt. % to 20 wt. %, even more preferred between 1wt. % and 8 wt. %.

Contacting the dielectric substrates with a solution containingorganosilanes according to method step (i). is performed by dipping orimmersing the substrates into said solution; or by spraying the solutionto the substrates. Contacting the substrate with a solution containingorganosilanes according to method step (i). is performed at least once.Alternatively said contacting can be performed several times, preferablybetween 2 to 10 times, more preferred between 2 to 5, even morepreferred between 1 to 3 times. Most preferred contacting is once totwice.

Contacting the substrate with a solution containing organosilanesaccording to method step (i). is performed for a time period rangingfrom 10 seconds to 20 minutes, preferred from 10 seconds to 10 minutes,most preferred from 10 seconds to 5 minutes.

Contacting the substrate with a solution containing organosilaneaccording to method step i. is performed at a temperature ranging from15 to 100° C., preferred from 20 to 50° C., most preferred from 23 to35° C.

The organosilane compound is preferably selected from the grouprepresented by the following formula

A_((4-x))SiB_(x)

-   -   wherein    -   each A is independently a hydrolyzable group,    -   x is 1 to 3, and    -   each B is independently selected from the group consisting of        C₁-C₂₀ alkyl, aryl, amino aryl and a functional group        represented by the formula

C_(n)H_(2n)X,

-   -   wherein    -   n is from 0 to 15, preferably 0 to 10 even more preferably 1 to        8, most preferably 1, 2, 3, 4 and    -   X is selected from the group consisting of amino, amido,        hydroxy, alkoxy, halo, mercapto, carboxy, carboxy ester,        carboxamide, thiocarboxamide, acyl, vinyl, allyl, styryl, epoxy,        epoxycyclohexyl, glycidoxy, isocyanato, thiocyanato,        thioisocyanato, ureido, thioureido, guanidino, thioglycidoxy,        acryloxy, methacryloxy groups; or X is a residue of a carboxy        ester; or X is Si(OR)₃, and wherein R is a C₁-C₅ alkyl group.

Preferably, the hydrolyzable group A is selected from the groupconsisting of —OH, —OR¹ and wherein R¹ is C₁-C₅ alkyl, —(CH₂)_(y)OR² andwherein y is 1, 2 or 3 and R² is H or C₁-C₅ alkyl, —OCOR³ and andwherein R³ is H or C₁-C₅ alkyl.

If B is an alkyl group it is preferably a C₁-C₁₀ alkyl, even morepreferred C₁-C₅ alkyl group like methyl, ethyl, propyl or isopropyl.Preferred aryl groups are phenyl- and benzyl-groups, either substitutedor unsubstituted. A preferred amino aryl group is —NH(C₆H₅).

Functional groups X within the meaning of this invention can be furtherfunctionalized. For example X=amino comprises alkylamine- or arylaminesubstituted amines like 3-(N-Styrylmethyl-2-aminoethylamino).

For the functional group X being Si(OR)₃, R preferably is methyl, ethyl,propyl or isopropyl.

Examples of particular classes of compounds within the formulas aboveare vinylsilanes, aminoalkylsilanes, ureidoalkylsilane esters,epoxyalkylsilanes and methacryloalkylsilane esters, in which thereactive organic functions are, respectively, vinyl, amino, ureido,epoxy and methacryloxy. Examples of the vinylsilanes arevinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxysilane,vinyl-tris-(beta(2)-methoxyethoxy) silane and vinyltriacetoxysilane. Asexamples of the aminoalkylsilanes, which are the preferred organosilanesfor use in the present invention, aregamma(3)-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,N-beta-(Aminoethyl)-gamma-aminopropyltrimethoxysilane, andN′-(beta-aminoethyl)-N-(beta-aminoethyl)-gamma-aminopropyltrimethoxysilane.A suitable ureidoalkylsilane ester is gammaureidoalkyltriethoxysilane,while suitable expoxyalkylsilanes arebeta-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane andgammaglycidoxypropyltrimethoxy silane. Useful methacryloxysilane estersare gamma-methacryloxypropyltrimethoxy silane andgamma-methacryloxypropyl-tris-(beta-methoxyethoxy) silane.

The at least one organosilane compound can either be a monomericorganosilane compound or an oligomeric organosilane compound which isobtained by a (partial) hydrolyzation and condensation of a monomericorganosilane compound according to the present invention prior to thedeposition onto the surface of the dielectric substrate.

The hydrolysis and condensation of organosilane compounds is well knownin the art. For example, the monomeric organosilane compound is reactedwith an acidic catalyst, for example, acetic acid or dilutedhydrochloric acid leading to a clear solution of an oligomericorganosilane compound derived from the monomeric organosilane compound.

Such oligomeric silanes derived from monomeric organosilane compoundaccording to the present by hydrolization shall be included into thescope of the present invention.

Optionally, the substrate can be heat treated after method step (i).Such treatment is generally performed at a temperature between 60-200°C., more preferred between 80-150° C. The treatment time can vary, e.g.between 1 and 30 minutes, preferred between 1 and 10 minutes.

Thereafter, the substrate is treated with a solution comprising anoxidizing agent in step (ii) selected from aqueous acidic or alkalinesolution of permanganate.

It was a surprisingly found that other oxidising agents thanpermanganate, for example a mixture of hydrogen peroxide and sulphuricacid or chromic acid are not suitable for a method according to thepresent invention, since they do not result in sufficient adhesionbetween the substrate and the subsequently plated metal layer. This wasunexpected since the prior art teaches that all oxidising agentsessentially result in the same surface modification.

Alkaline solutions of permanganate, e.g. sodium or potassiumpermanganate are preferred. The solution preferably contains 20-100 g/lpermanganate ions and 10-40 g/l hydroxide ions. A preferred hydroxideion source is sodium or potassium hydroxide.

Contacting the dielectric substrates with a solution containing anoxidizing agent according to method step (ii) is performed by dipping orimmersing the substrates into said solution; or by spraying the solutionto the substrates.

Contacting the substrate with a solution containing an oxidizing agentaccording to method step (ii) is performed for a time period rangingfrom 30 seconds to 30 minutes, preferred from 30 seconds to 10 minutes.

Contacting the substrate with a solution containing an oxidizing agentaccording to method step (ii) is performed at a temperature ranging from20 to 95° C., preferred from 50 to 85° C.

In one embodiment of the present invention the method comprises thefollowing steps:

-   -   (i) treating said surface with a solution comprising at least        one organosilane compound for a period of time of between 10 s        and 10 min. at a temperature of between 15 and 50° C.    -   (ii) treating said surface with a solution comprising an        oxidizing agent selected from an alkaline aqueous solution of        permanganate ions in a concentration of 20-100 g/l for a period        of time of between 1 and 30 min. at a temperature of between 20        and 95° C. to obtain a roughened surface having an average        surface roughness Ra of less than 150 nm.

A surface roughness Ra of less than 150 nm can be between 50 and 150 nm,preferably between 60 and 130 nm and even more preferably between 70 and120 nm.

Various kinds of dielectric substrates can be metallized with a methodaccording to the present invention. Metallization is performed by a wetchemical plating method. Such plating method comprises electroless,immersion and electrolytic plating processes, usually performed inaqueous solution.

The dielectric substrates to be metallized can be selected from thegroup comprising plastics, plastic-glass, and plastic-ceramiccomposites.

Plastics can be selected from the group comprisingacrylnitrile-butadiene-styrol-copolymer (ABS copolymer); polyamide; amixture of an ABS copolymer and at least one other polymer which isdifferent to the ABS copolymer; polycarbonate (PC); ABS/PC blends; epoxyresin; bismaleimide-triazine resin (BT); cyanate ester resin; polyimide;polyethylene terephthalate (PET); polybutylene terephthalate (PBT);polylactic acid (PLA); polypropylene (PP); and polyester.

Also, dielectric substrates used in the manufacture of printed circuitboards can be used. Such material typically consists of epoxy basedmaterial, for example epoxy blends like epoxy-benzotriazole blends,epoxy-cyanate-blends, epoxy-propylene blends, or epoxy-polyimide blends.

For step (iii) several methods for plating a metal onto a substrate byapplying a wet-chemical plating method are known to the person skilledin the art. According to the present invention the wet chemical platingmethod preferably is an electrolytic plating method, an immersionplating process or an electroless plating method.

Dielectric substrates, e.g. plastic objects can then be metallized afteractivation by using an electroless metallising method or alternativelyby using a direct plating method (electrolytic plating method). Theobject is first cleaned followed by application of e.g. a noble metal orconductive polymer and then finally metallised.

A typically activation of dielectric substrates like printed circuitboards for subsequent metal plating is performed as follows:

Preferably, the first conductive layer comprises copper and is depositedby electroless plating. Preferably in this case, the substrate isactivated by e.g., deposition of a noble metal containing colloid or asolution comprising noble metal ions prior to electroless deposition ofcopper. The most preferable activation is by deposition of palladium-tincolloids or palladium ions. Such methods are established in the arts andknown to the skilled person.

Instead of copper the first conductive layer can comprise nickel.

An exemplary and non-limiting pretreatment process, especially forprinted circuit board laminates and other suitable substrates, maycomprise the following steps

-   -   a) contacting the substrate with an activator solution, that        contains colloidal or ionic catalysing metal, such as a noble        metal, preferably palladium, causing the the substrate's surface        to become catalytic,    -   and optionally, particularly if the activator contains ionic        catalysing metal,    -   b) contacting the substrate with a reducer, wherein the metal        ions of an ionic activator are reduced to elemental metal,    -   or, if the activator contains colloidal catalysing metal,    -   c) contacting the substrate with an accelerator, wherein the        components of the colloid, for example a protective colloid, is        removed from the catalysing metal.

The method according to the present invention is particularly suitablefor manufacture of fine line circuitry. This is shown in FIG. 1.

A method for manufacture of fine line circuitry known in the art is thesemi-additive process (SAP) which starts from a bare dielectric build-uplayer (1) having on at least a portion of the back side a copper areawhich can be for example a contact area (2), and a second dielectriclayer (3) attached to the back side of the dielectric build-up layer(1). Such a substrate is shown in FIG. 1 a. At least one opening (4)such as a blind micro via is formed by e.g. laser drilling in thebuild-up layer (1) which extends through the substrate to the copperarea (2) on the back side of the build-up layer (1) (FIG. 1 b). Thedielectric surface of the build-up layer (1) is subjected to a desmearprocess in the next step which leads to a roughened top surface (5 a) ofthe build-up layer (1) and a roughened surface (5 b) of the dielectricside walls of the at least one opening (4) (FIG. 1 c).

Further activation of the roughened top surface (5 a) and the roughenedside walls (5 b) by e.g. depositing a noble metal containing activatoris necessary for successive electroless plating of copper. Next, aconductive seed layer (6), generally made of copper, is deposited byelectroless plating onto the roughened top surface (5 a) of the build-uplayer (1) and the roughened side walls (5 b) of the at least one opening(4) (FIG. 1 d). Such a conductive layer (6) usually has a thickness of0.8 μm to 1.5 μm which is a) required to provide a sufficient electricalconductivity on the roughened top surface (5 a) for successiveelectroplating of copper and b) to ensure that during electrolessplating of copper also a sufficient electrical conductivity is providedto the roughened side walls (5 b) of the at least one opening (4).

A thicker layer of copper (8) is then selectively electroplated intoopenings of a patterned resist layer (7) onto the roughened andactivated top surface of the build-up layer (1) and the roughened andactivated dielectric walls of the at least one opening (4) (FIG. 1 e tof). The patterned resist layer (7) is removed (FIG. 1 g) and thoseportions of the conductive layer (6) which are not covered byelectroplated copper (8) are removed by differential etching (FIG. 1 h).Such a process is for example disclosed in U.S. Pat. No. 6,278,185 B1and U.S. Pat. No. 6,212,769 B1.

A method for manufacturing fine line circuitry on a printed circuitboard comprises, in this order, the following steps

-   -   (i) Providing a substrate comprising a bare dielectric build-up        layer (1) having on at least a portion of the back side a        contact area (2) and a second dielectric layer (3) attached to        the back side of the build-up layer (1),    -   (ii) Forming at least one opening (4) in the build-up layer (1)        which extends through the substrate to the contact area (2),    -   (iii) Treating said surface with a solution comprising at least        one organosilane compound,    -   (iv) Treating said surface with a solution comprising an        oxidizing agent,    -   (v) Depositing a conductive seed layer (6) onto the top surface        (5 a) of the dielectric build-up layer (1) and the dielectric        side walls (5 b) of the at least one opening (4), and    -   (vi) Selectively depositing a copper layer (8) into openings of        a patterned resist layer (7) by electroplating.

Dielectric substrates, e.g. plastic objects can then be metallized afteractivation by using an electroless metallising method or alternativelyby using a direct plating method (electrolytic plating method). Theobject is first cleaned followed by application of e.g. a noble metal orconductive polymer and then finally metallised.

A typically activation of dielectric substrates for subsequent metalplating is performed as follows:

The plastic is activated for electroless metallisation using anactivator which contains a noble metal and then electrolesslymetallised. A thicker metal layer can then also be appliedelectrolytically afterwards. In the case of the direct plating method,the etched surface is usually treated with a palladium colloid solutionand then with an alkaline solution which contains copper ions forming acomplex with a complexing agent. Thereafter the object can then beelectrolytically metallised directly (EP 1 054 081 B1).

A suitable metallizing sequence in step (iii) would involve thefollowing steps:

-   -   A) treatment with a solution of a colloid or with a compound,        particularly a salt of a metal of Group VIIIB or IB of the        Periodic Table of the Elements (noble metal), particularly a        palladium/tin colloid;        -   and    -   B) electrolytic metallization using a metallising solution,

In one embodiment of the invention the substrate is a dielectricsubstrate and the step

-   -   iii. metal plate the substrate applying a wet-chemical plating        method; comprises:    -   iiia. contacting the substrate with a noble metal colloid or a        noble metal ion containing solution;    -   iiib. contacting the substrate with an electroless metal plating        solution; and    -   iiic. contacting the substrate with an electrolytic metal        plating solution.

In one embodiment of the invention at least one of the followingadditional method steps are performed in the overall process step iii.

-   -   iii1. Dipping the objects or the substrates in a pre-dipping        solution;    -   iiia1. Rinsing the objects or the substrates in a rinsing        solution;    -   iiia2. Treating the objects or the substrates in an accelerating        solution or in a reducing agent solution;    -   iiib1. Rinsing the objects or the substrates in a rinsing        solution; and    -   iiic1. Rinsing the objects or the substrates in a rinsing        solution.

In this preferred embodiment these further method steps are carried outwhen the objects or the substrates are to be metallised using anelectroless metallisation method which means that a first metal layer isapplied on the objects or the substrates using an electroless method.

The accelerating solution preferably serves to remove components of thecolloid solution according to method step iiia., for example aprotective colloid. If the colloid of the colloid solution according tomethod step iia. is a palladium/tin colloid, a solution of an acid ispreferably used as an accelerating solution, for example sulfuric acid,hydrochloric acid, citric acid or also tetrafluoroboric acid, in orderto remove the protective colloid (tin compounds).

The reducing agent solution is used if a solution of a noble metal ionis used in method step (ii)a., for example a hydrochloric acid solutionof palladium chloride or an acid solution of a silver salt. The reducingagent solution in this case is also a hydrochloric acid solution and,for example, contains tin(II) chloride, or it contains another reducingagent such as NaH₂PO₂ or a borane or boron hydride, such as an alkali orearth alkali borane or dimethylaminoborane.

On the other hand, a method is preferred in which the objects or thesubstrates are not metallised electrolessly but are to be directlymetallised using an electrolytic metallisation process (withoutelectroless metallisation).

In this embodiment of the invention the substrate is a dielectricsubstrate and the step

iii. metal plate the substrate applying a wet-chemical plating method;comprises:

-   -   iiia. contacting the substrate with a noble metal colloid;    -   iiib. contacting the substrate with a conversion solution so        that a sufficiently electrically conductive layer is formed on        the surface of the substrate for direct electrolytic        metallisation; and    -   iiic. contacting the substrate with an electrolytic metal        plating solution.

The method steps iiid., iiie. and iiif. are performed in the sequencegiven, but not necessarily immediately one after the other. For example,a plurality of rinsing steps can be performed after said method steps.In this embodiment the method steps iid. and iie. act as an activationstep.

The conversion solution preferably serves to create a sufficientlyelectrically conductive layer on the surface of the objects or thesubstrates in order to subsequently allow direct electrolyticmetallisation, without preceding electroless metallisation. If thecolloid of the colloid solution according to method step iid. is apalladium/tin colloid then an alkaline solution containing copper ionscomplexed with a complexing agent is preferably used as a conversionsolution. For example the conversion solution can contain an organiccomplexing agent such as tartaric acid or ethylenediaminetetraaceticacid and/or one of its salts, such as a copper salt, such as coppersulfate:

The conversion solution can comprise:

(i) a Cu(II), Ag, Au or Ni soluble metal salt or mixtures thereof,(ii) 0.05 to 5 mol/l of a group IA metal hydroxide and(iii) a complexing agent for an ion of the metal of said metal salt

The treatment liquids described below are preferably aqueous.

In a preferred embodiment of the invention the solution of the colloidof the noble metal of Group VIIIB or IB of the Periodic Table of theElements used in the activation step is an activator solution containinga palladium/tin colloid. This colloid solution preferably containspalladium chloride, tin(II) chloride and hydrochloric acid or sulfuricacid. The concentration of the palladium chloride is preferably 5-200mg/l, particularly preferred 20-100 mg/l and most preferred 30-60 mg/l,based on Pd²⁺. The concentration of the tin(II) chloride is preferably0.5-20 g/l, particularly preferred 1-10 g/l and most preferred 2-6 g/l,based on Sn²⁺. The concentration of the hydrochloric acid is preferably100-300 ml/l (37% by weight of HCl). Furthermore, a palladium/tincolloid solution also preferably contains tin(IV) ions which aregenerated through oxidation of the tin(II) ions. The temperature of thecolloid solution is preferably 20-50° C. and particularly preferred30-40° C. The treatment time is preferably 0.5-10 min, particularlypreferred 2-5 min and most preferred 3.5-4.5 min.

As an alternative the colloid solution can also contain another metal ofGroup VIIIB or IB of the Periodic Table of the Elements, for exampleplatinum, iridium, rhodium, gold or silver or a mixture of these metals.It is basically possible for the colloid not to be stabilised with tinions as a protective colloid but rather another protective colloid beingused instead, for example an organic protective colloid like polyvinylalcohol.

If a solution of a noble metal ion is used instead of a colloid solutionin the activation step, preferably a solution is used which contains anacid, in particular hydrochloric acid, and a noble metal salt. The noblemetal salt can, for example, be a palladium salt, preferably palladiumchloride, palladium sulfate or palladium acetate, or a silver salt, forexample silver acetate. As an alternative a noble metal complex can alsobe used, for example a palladium complex salt such as a salt of apalladium-amino complex. The noble metal compound is present, forexample, in a concentration of 20 mg/l to 200 mg/l, based on the noblemetal, for example based on Pd²⁺. The solution of the noble metalcompound can be used at 25° C. or at a temperature from 15° C. to 70° C.

Before bringing the objects or the substrates in contact with thecolloid solution, the objects or the substrates are preferably firstbrought into contact with a pre-dipping solution which has the samecomposition as the colloid solution but without the metal of the colloidand its protective colloid, which means that this solution, in the caseof a palladium/tin colloid solution, just contains hydrochloric acid ifthe colloid solution also contains hydrochloric acid. The objects or thesubstrates are brought directly into contact with the colloid solutionafter treatment in the pre-dipping solution, without rinsing off theobjects or the substrates.

After treating the objects or the substrates with the colloid solutionthese are typically rinsed and then brought into contact with theaccelerating solution in order to remove the protective colloid from thesurface of the objects or the substrates.

If the objects or the substrates are treated with a solution of a noblemetal ion instead of a colloid solution they will be subjected to areduction treatment after first being rinsed. The reducing agentsolution used for these cases typically contains hydrochloric acid andtin(II) chloride. If the solution of the noble metal compound is ahydrochloric acid solution of palladium chloride. It is, however,preferable to use an aqueous solution of NaH₂PO₂. Moreover, if thesolution of the noble metal compound is a neutral or alkaline solutionof a complex stabilized Pd sulphate or chloride, it is preferable to usean aqueous solution of DMAB (dimethyl aminoborane) or sodium borohydridein the reduction treatment.

For electroless metallisation, the objects or the substrates can firstbe rinsed after the acceleration or treatment with reducing agentsolution and then electrolessly plated with nickel, for example. Aconventional nickel bath will serve to do this which, for example,contains a number of substances including nickel sulfate, ahypophosphite, for example sodium hypophosphite, as a reducing agent,and organic complexing agents and pH adjusting agents (for example abuffer).

As an alternative, an electroless copper bath can be used whichtypically contains a copper salt, for example copper sulfate or copperhypophosphite, and also a reducing agent such as formaldehyde or ahypophosphite salt, for example an alkali or ammonium salt, orhypophosphorous acid, and also one or more complexing agents such astartaric acid, as well as a pH adjusting agent such as sodium hydroxide.

Any metal depositing baths can be used for the subsequent electrolyticmetallisation, for example for depositing nickel, copper, silver, gold,tin, zinc, iron, lead or their alloys. This type of depositing bath iswell known to the person skilled in the art. A Watts nickel bath isnormally used as a bright nickel bath which contains nickel sulfate,nickel chloride and boric acid as well as saccharine as an additive. Asa bright copper bath a composition is used which, for example, containscopper sulfate, sulfuric acid, sodium chloride as well as organic sulfurcompounds, in which the sulfur is present in a low oxidation stage, forexample as an organic sulfide or disulfide, as additives.

If a direct electroplating process is used, that is, a first metal layeris not deposited electrolessly but rather after treatment of the objectsor the substrates with the conversion solution and depositedelectrolytically after the optional subsequent rinsing treatment, thenan electrolytic metallisation bath is used, for example a nickel strikebath, which is preferably composed on the basis of a Watts nickel bath.These types of baths for example contain nickel sulfate, nickel chlorideand boric acid and saccharine as an additive.

Treatment of the objects or the substrates according to the methodaccording to the invention is preferably performed in a conventionaldipping process in which the objects or the substrates are dippedsubsequently in solutions in containers in which the respectivetreatment takes place. In this case the objects or the substrates caneither be fastened to racks or filled into drums and dipped in thesolutions. Fastening to racks is preferred because a more directedtransmission of the ultrasound energy to the objects or the substratesis possible via the racks. Alternatively, the objects or the substratescan be treated in so-called conveyorized processing plants in which theylay, for example, on racks and are continuously transported in ahorizontal direction through the plant and treated with ultrasound, asrequired.

In another embodiment of the present invention direct metallization canbe obtained by employing a conductive polymer to the surface of adielectric substrate as for example described in US 2004/0112755 A1,U.S. Pat. No. 5,447,824, and WO 89/08375 A.

EP 0 457 180 A2 discloses a method for metallizing dielectricsubstrates, this method comprising first forming a manganese dioxidelayer on the substrate and then treating the surfaces with an acidicsolution containing pyrrole and methane sulfonic acid. Instead ofpyrrole the solution may also contain thiophene. Due to this treatmentan electrically conducting polymer layer is formed. This electricallyconducting layer may finally be electrolytically metallized.Alternatively, thiophene and aniline instead of pyrrole can be applied.Such method is suitable to be used as an activation step andsubsequently to metallize non conductive substrates according to thepresent invention.

In this embodiment of the invention the substrate is a dielectric andthe following further method steps are performed for metallization ofthe substrate in step iii.:

-   iiic. bringing the substrate into contact with a water-soluble    polymer;-   iiid. treating the substrate with a permanganate solution;-   iiie. treating the substrate with an acidic aqueous solution or an    acidic microemulsion of aqueous base containing at least one    thiophene compound and at least one alkane sulfonic acid selected    from the group comprising methane sulfonic acid, ethane sulfonic    acid and ethane disulfonic acid;    and the step-   iv. metal plate the substrate applying a wet-chemical plating    method;    comprises:-   ivb. contacting the substrate with an electrolytic metal plating    solution.

The water-soluble polymer used in step ic. preferably is selected fromthe group consisting of polyvinyl amine, polyethylene imine, polyvinylimidazole, alkylamine ethylene oxide copolymers, polyethylene glycol,polypropylene glycol, copolymers of ethylene glycol and polypropyleneglycol, polyvinyl alcohol, polyacrylates, polyacrylamide,polyvinylpyrrolidone and mixtures thereof. The concentration of thewater-soluble polymer ranges from 20 mg/l to 10 g/l.

The solution of a water-soluble polymer may further contain awater-soluble organic solvent selected from the group consisting ofethanol, propanol, ethylene glycol, diethyleneglycol, glycerine, dioxin,butyrolacton, N-methyl pyrrolidone, dimethyl formamide,dimethylacetamide, half ethers and half esters of ethylene glycol. Thewater-soluble organic solvent may be utilized either in pure form ordiluted with water. The concentration of the water-soluble organicsolvent ranges from 10 ml/l to 200 ml/l. The solution of a water-solublepolymer is held at a temperature in the range of 25° C. to 85° C. andthe dielectric substrate is immersed in this solution for 15 s to 15 minduring step ic.

Next, the dielectric substrate is treated with a permanganate solutionin step id. The source of permanganate ions can be any water-solublepermanganate compound. Preferably the source of permanganate ions isselected from sodium permanganate and potassium permanganate. Theconcentration of permanganate ions ranges from 0.1 mol/l to 1.5 mol/l.The permanganate solution can be either acidic or alkaline. Preferably,the permanganate solution has a pH value in the range of 2.5 to 7. Bymeans of step id. a layer of MnO₂ is formed on the side walls of a blindmicro via (BMV).

The substrate is then contacted in step ie. with a solution comprisingpreferably a thiophene compound and an alkane sulfonic acid.

The thiophene compound is preferably selected from 3-heterosubstitutedthiophenes and 3,4-heterosubstituted thiophenes. Most preferably, thethiophene compound is selected from the group consisting of 3,4-ethylenedioxythiophene, 3-methoxy thiophene, 3-methyl-4-methoxy thiophene andderivatives thereof. The concentration of the thiophene compound rangesfrom 0.001 mol/l to 1 mol/l, more preferably from 0.005 mol/l to 0.05mol/l.

The alkane sulfonic acid is selected from the group comprising methanesulfonic acid, ethane sulfonic acid, methane disulfonic acid, ethanedisulfonic acid and mixtures thereof. The concentration of the alkanesulfonic acid is set by adjusting the desired pH value of the solutionutilized in step ie. Preferably the pH value of said solution is set inthe range of 0 to 3, more preferably in the range of 1.5 to 2.1.

For the purposes of the present invention plating of copper as metal isparticularly preferred. In printed circuit board applications the totalthickness of the deposited a copper layer or layers generally rangesbetween 1 and 50 μm, more preferably between 4 and 30 μm.

Examples

The following experiments are meant to illustrate the benefits of thepresent invention without limiting its scope.

In the experiments the different silanes employed are listed andidentified in Table 1. The following organic solvents were used todissolve the silanes: isopropanol (bp 82° C.: denoted in the followingas IPA), and 2-isopropoxyethanol (bp 142° C., in the following denotedas IPPE).

Sample Nos. P1, P6 through P9, and P11 through P 20 were first treatedwith a silane composition and then treated in an aqueous solutioncontaining MnO₄-ions. For sample No. P2 the process sequence waschanged: treatment in an aqueous solution containing MnO₄-ions was firstand then followed by treatment in the silane composition (comparativeexample). For sample No. P3 the treatment in an aqueous solutioncontaining MnO₄-ions was omitted and only the silane composition wasapplied (also comparative example). Sample No. P4 was processed in anaqueous solution containing MnO₄-ions only, without any silane treatment(comparative example). Samples Nos. P5 and P10 were first treated withthe solvent matrix without the silane compound and then treated in anaqueous solution containing MnO₄-ions (comparative examples). Thepermanganate treatment step was always followed by a reducer step toremove the manganese(IV)oxide. The corresponding process conditions areprovided in Table 1.

Compositions are provided in Table 1. Treatment time was 1 min atambient temperature.

The base material used was an epoxy resin ABF GX92 from Ajinomoto Co.;Inc. For the experiments, samples (7.5×15 cm) were cut out of panelslaminated and pre-cured for 30 minutes at a temperature of 100° C.followed by 30 minutes at a temperature of 180° C.

All solutions were freshly made up before spraying. Silane content isgiven in weight percent and was 3 wt. % for all experiments performed.

Silane application: The solution (excluding example P4) was sprayed ontothe substrate using the ExactaCoat spray device by Sonotek. For examplesP5 and P10 the solvent does not contain a silane and was applied thesame way. Following parameters were set for all investigations:

Flow rate: 1.4 ml/min. (6 ml/min.)

Nozzle Distance: 4 cm

Nozzle Speed: 40 mm/s

Overlap: 14.2 mm

Nitrogen flow: 0.8-1.0 mPa

One Spray Cycle

Afterwards the panels were held for 10 minutes before baking them at105° C. for 5 min. Panels were allowed to cool down to room temperatureand passed to the permanganate etchant (excluding sample P3).

Sample P2 was first processed through the permanganate etchant andreduction solution and sprayed afterwards. No second MnO₄-etch step wasincluded.

Additional comparative examples P21 and P22 have been carried out insolutions containing sulphuric acid and hydrogen peroxide.

Example P21 was performed according to the foregoing process sequencewherein the solution comprising an oxidizing agent contained in a volumeratio of 3 to 1 concentrated sulphuric acid and 30 wt. % hydrogenperoxide. Treatment was performed at a temperature of 60° C. for 10seconds. Despite obtaining a rather high roughness value subsequentmetal plating resulted in a very poor adhesion of the metal layer to thesurface substrate, thus rendering this treatment method unsuitable toproduce an adherent metal layer which is the purpose of the presentinvention. Higher treatment time and/or higher temperatures resulted incomplete removal of the resin layer and no adhesion of the subsequentlyplated metal layer. Example P22 was performed according to the foregoingprocess sequence wherein the solution comprising an oxidizing agentcontained 20 mL/L concentrated sulphuric acid and 20 mL/L 30 wt. %hydrogen peroxide. Treatment was performed at a temperature of 25° C.for 5 minutes. The surface treated showed a low roughness and very pooradhesion of the subsequently plated metal layer, rendering this solutionto produce an adherent metal layer which is the purpose of the presentinvention.

TABLE 1 Sample names and process conditions. Peel Average Exp. SilaneStrength Roughness No. (3% wt.) Solvent Treatment N/cm (Ra) nm P13-Aminopropyltri- IPA 1. Silane; 5.53 102 ethoxysilane 2. MnO4 + ReducerP2* Aminopropyltri- IPA 1. MnO4 + Reducer; 0.86 96 ethoxysilane 2.Silane P3* Aminopropyltri- IPA only Silane 0.08 80 ethoxysilane P4* NoNo only MnO4 + Reducer 0.78 96 P5* No IPA 1. only Solvent Treat- 2.00 95ment; 2. MnO4 + Reducer P6 3-Glycidoxypropyl- IPA 1. Silane; 7.33 82trimethoxysilane 2. MnO4 + Reducer P7 Vinyl tris(2- IPA 1. Silane; 4.490 methoxyethoxy) 2. MnO4 + Reducer silane P8 N-Styryl-methyl-2- IPA 1.Silane; 7.0 109 aminoethylamino)- 2. MnO4 + Reducer propyltrimethoxy-silane P9 1-[2-(Trimethoxy- IPA 1. Silane; 4.6 76 silyl)ethyl]cyclo- 2.MnO4 + Reducer hexane-3,4-epoxide P10* No IPPE 1. only Solvent Treatment3.0 77 2. MnO4 + Reducer P11 3-Aminopropyltri- IPPE 1. Silane; 6.9 94ethoxysilane 2. MnO4 + Reducer P12 3-Chloropropyltri- IPPE 1. Silane;5.30 95 methoxysilane 2. MnO4 + Reducer P13 3-Glycidoxypropyl- IPPE 1.Silane; 7.0 96 trimethoxysilane 2. MnO4 + Reducer P14 Vinyl tris (2-IPPE 1. Silane; 6.9 98 methoxyethoxy) 2. MnO4 + Reducer silane P15Ethyltriacetoxy- IPPE 1. Silane; 5.5 93 silane 2. MnO4 + Reducer P163-(Trimethoxy- IPPE 1. Silane; 5.4 87 silyl)propyl- 2. MnO4 + Reducermethacrylate P17 N-Styrylmethyl-2- IPPE 1. Silane; 7.0 113aminoethylamino) 2. MnO4 + Reducer propyl- trimethoxysilane P18Phenyltrimethoxy- IPPE 1. Silane; 4.7 76 silane 2. MnO4 + Reducer P191-[2-(Trimethoxy- IPPE 1. Silane; 5.2 88 silyl)ethyl] cyclo- 2. MnO4 +Reducer hexane-3,4 epoxide P20 1-[3-(Trimethoxy- IPPE 1. Silane; 8.0 109silyl)propyl]urea 2. MnO4 + Reducer P21* 3-Aminopropyltrieth- IPA 1.Silane; 2.1 130 oxysilane 2. H2SO4/H2O2 P22* 3-Aminopropyltrieth- IPA 1.Silane; 1.3 67 oxysilane 2. H2SO4/H2O2 *comparative Examples MnO4denotes MnO₄ ⁻⁻ ions

FIG. 2 shows a surface after permanganate treatment of GX92 substratematerial according to example P20. Measurement was performed on a ZeissGemini SEM, voltage 5 kV, magnification: 5000×.

The roughness Ra measured was 109 nm measured by an Olympus LEXT 3000confocal laser microscope.

FIG. 3 shows an SEM image of a surface after permanganate treatmentwithout prior application of a silane of GX92 substrate material. Thiscorresponds to a method known in the art involving a waterbased Swellerfollowed by Permanganate-Etching. Permanganate concentration was 60 g/l,NaOH conc. 45 g/l, treatment time 20 minutes, and temperature 80° C. Theroughness Ra measured by above mentioned confocal laser microscope was200 nm. Such roughness can be too high for manufacture of fine linecircuitry.

Thereafter, the samples were metal plated according to the processparameters provided in Table 2. Table 2 comprises of the processsequence applied to finally deposit 0.8 μm of electroless copper and 30μm electrolytically deposited copper on GX92 substrate material.

TABLE 2 Parameters used for subsequent metal plating Step No. Name T [°C.] t [min] 1 Permanganate Etch 75 15 (45 g/l MnO₄ ⁻, 45 g/l NaOH) DIRinse 2 MnO₄ Reduction sol. 50 4 DI Rinse 3 Cleaner 60 4 DI Rinse 4NaPS/H₂SO₄ 35 1 DI Rinse 5 Pre-Dip 25 1 6 Neoganth Activator 40 4 DIRinse 7 Neoganth Reducer 30 3 DI Rinse 8 Electroless Cu 34 15 DI Rinse,air dry 9 Electroless Cu An- 150 30 nealing 10 H₂SO₄ Pre-Dip 25 1 11Acid Cu 25 90 Current Density: 2 A/dm² Copper Thickness: 30 μm DI Rinse,air dry 12 Acid Cu Annealing 180 60

Peel strength measurements of the plated metal layer to the substratewere performed by routing the samples in stripes of 1 cm width and 3 cmlength after final annealing. Peel strength measurements were performedwith an Erichsen Wuppertal 708 strain gauge using a Chatillon LTCM-6pulling mechanism The adhesion values for all samples are depicted inTable 1, 5^(th) (“Peel”) column.

Field Emission Scanning Electron Microscopy (FE-SEM) was performed usinga LEO 1530 with 5 kV accelerating voltage and a silicon drift detector(Xmas 80, Oxford). Images were recorded with a magnification of 5000.Dielectric surface was measured after etching the plated copper usingsulphuric acid/hydrogen peroxide (50 ml/L conc. H₂SO₄, 53 ml/L H₂O₂ inwater at 40° C.). Samples were sputtered with Iridium beforemeasurement.

For commercial processes, for example flip-chip ball-grid-arrays,typically adhesion values of greater than 4-5 N/cm are required. Thisdepends on the type of application.

Average roughness values (Ra) were measured on an Olympus LEXT 3000confocal laser microscope. Roughness values were gathered over a surfacearea of 120 μm by 120 μm. The average roughness values (Ra) for allsamples are depicted in Table 1, 6^(th) column (Average Roughness Ra).

Sufficient adhesion between the plated metal layer and the substratecould only be obtained by treatment of the samples with a processaccording to the present invention, i.e. a silane-based treatment of thesubstrate surface first which is followed by the permanganate treatmentstep. All other combinations of the process sequence as shown in Table 1result in very low adhesion of the plated metal layer which is notacceptable for commercial applications.

The lowest adhesion values were found for the sample P3 coated withsilanes only (without any permanganate treatment) and then subsequentlymetallized. A slightly increase of initial adhesion was seen when thepermanganate treatment was applied before the metal plating steps of thesubstrate (Sample No. P4). This increase was caused by an additionalroughening of the surface due to the permanganate step. However, allsamples which were not processed through permanganate after the silanecoating showed blister on the surface after the final copper annealing.Therefore a permanganate rinse is preferable after the silane coating.

By changing the first two main steps in the process sequence it wasdemonstrated that only the correct sequence (first silane treatmentfollowed by permanganate cleaner) resulted in significant adhesionincrease (up to 5.5 N/cm). All other combinations (silane only, MnO₄only as well as first MnO₄ then silane treatment) gave very low adhesion<1.0 N/cm.

The low roughness values of the treated samples render the processsuitable for manufacture of circuit traces which are smaller than 10 umwidth. For such structures surface roughness values over 150 nm werehitherto required to achieve sufficient adhesion between the substrateand the plated metal layer. However, average roughness values higherthan 150 nm may be too high for circuit traces smaller than 10 um inwidth.

1. A method for treating a surface of a dielectric substrate to preparesaid surface for subsequent wet chemical metal plating, such methodcomprising in this order the steps of (i) treating said surface with asolution comprising at least one organosilane compound; (ii) treatingsaid surface with a solution comprising an oxidizing agent selected fromaqueous acidic or alkaline solutions of a permanganate salt.
 2. Methodaccording to claim 1 wherein the concentration of permanganate saltranges from 20-100 g/l.
 3. Method according to claim 1 wherein theorganosilane compound is selected from the group represented by theformulaA_((4-x))SiB_(x) wherein each A is independently a hydrolyzable group, xis 1 to 3, and each B is independently selected from the groupconsisting of C₁-C₂₀ alkyl, aryl, amino aryl and a functional grouprepresented by the formulaC_(n)H_(2n)X, wherein n is from 0 to 15, preferably 0 to 10 even morepreferably 1 to 8, most preferably 1, 2, 3, 4 and X is selected from thegroup consisting of amino, amido, hydroxy, alkoxy, halo, mercapto,carboxy, carboxy ester, carboxamide, thiocarboxamide, acyl, vinyl,allyl, styryl, epoxy, epoxycyclohexyl, glycidoxy, isocyanato,thiocyanato, thioisocyanato, ureido, thioureido, guanidino,thioglycidoxy, acryloxy, methacryloxy groups; or X is a residue of acarboxy ester; or X is Si(OR)₃, and wherein R is a C₁-C₅ alkyl group. 4.Method according to claim 3 wherein the hydrolyzable group A is selectedfrom the group consisting of —OH, —OR¹ and wherein R¹ is C₁-C₅ alkyl,—(CH₂)_(y)OR² and wherein y is 1, 2 or 3 and R² is H or C₁-C₅ alkyl,—OCOR³ and and wherein R³ is H or C₁-C₅ alkyl.
 5. Method according toclaim 4, wherein R¹, R² and R³ are independently selected from methyl,ethyl, propyl and isopropyl.
 6. Method according to claim 1 wherein theorganosilane compound is selected from the group consisting ofvinylsilanes, aminoalkylsilanes, ureidoalkylsilanes, methacryloxysilanes and epoxyalkylsilanes.
 7. Method according to claim 1 whereinthe organosilane is applied in a concentration of between 0.5 wt. % and20 wt. %.
 8. Method according to claim 1 wherein the organosilane isdissolved in a polar organic solvent organic solvent having boilingpoint in the range of 60 to 250° C.
 9. Method according to claim 1wherein the organosilane is dissolved in a polar organic solventselected from diethyleneglycol, 2-isopropoxyethanol (IPPE),di(propyleneglycol)methyletheracetate (DPGMEA), and 2-ethyl-1-hexanol.10. Method according to claim 1 wherein the oxidizing agent according tostep 1 ii) is an alkaline aqueous solution of permanganate ions. 11.Method according to claim 1, wherein (i) treating said surface with asolution comprising at least one organosilane compound is carried outfor a period of time of between 10 s and 10 min. at a temperature ofbetween 15 and 50° C., and (ii) treating said surface with a solutioncomprising an oxidizing agent selected from an alkaline aqueous solutionof permanganate salt is carried out in a concentration of 20-100 g/l fora period of time of between 1 and 30 min. at a temperature of between 20and 95° C. to obtain a roughened surface having an average surfaceroughness Ra of less than 150 nm.
 12. Method according to claim 1further comprising (iii) metallizing the substrate after step (ii) witha wet chemical plating method.
 13. Method according to claim 12 whereinmetallizing is a copper metallizing.
 14. Method according to claim 13wherein (iii) metallizing the substrate after step (ii) with a wetchemical plating method comprises the following steps to render thesurface conductive (iii a) contacting the substrate with an activatorsolution, that contains colloidal or ionic catalysing metal causing thesubstrate's surface to become catalytic, and optionally, particularly ifthe activator contains ionic catalysing metal, (iii b) contacting thesubstrate with a reducer, wherein the metal ions of an ionic activatorare reduced to elemental metal, or, if the activator contains colloidalcatalysing metal, (iii c) contacting the substrate with an accelerator,wherein the components of the colloid, for example a protective colloid,is removed from the catalysing metal.
 15. Method according to claim 1wherein the dielectric substrate is a substrate comprising a baredielectric build-up layer having a back side and a top surface, havingon at least a portion of the back side a contact area and a seconddielectric layer attached to the back side of the build-up layer, havingat least one opening in the build-up layer which extends through thesubstrate to the contact area, (i) treating said surface with a solutioncomprising at least one organosilane compound as defined in claim 1,(ii) treating said surface with a solution comprising an oxidizing agentas defined in claim 1, (iii) depositing a conductive seed layer onto thetop surface of the dielectric build-up layer and the dielectric sidewalls of the at least one opening, and selectively depositing a copperlayer into openings of a patterned resist layer by electroplating. 16.The method of claim 14 wherein the ionic catalysing metal is a noblemetal.
 17. Method according to claim 12 wherein (iii) metallizing thesubstrate after step (ii) with a wet chemical plating method comprisesthe following steps to render the surface conductive (iii a) contactingthe substrate with an activator solution, that contains colloidal orionic catalysing metal causing the the substrate's surface to becomecatalytic, and optionally, particularly if the activator contains ioniccatalysing metal, (iii b) contacting the substrate with a reducer,wherein the metal ions of an ionic activator are reduced to elementalmetal, or, if the activator contains colloidal catalysing metal, (iii c)contacting the substrate with an accelerator, wherein the components ofthe colloid, for example a protective colloid, is removed from thecatalysing metal.
 18. The method of claim 17 wherein the ioniccatalysing metal is a noble metal.